Polycarbonate resin has a high refractive index and excellent transparency and impact resistance and is now widely used as a material for lenses, especially spectacle lenses. Since spectacle lenses made of polycarbonate resin are thinner and lighter than existing glass lenses and plastic lenses manufactured by cast polymerization (to be referred to as “cast lenses” hereinafter) and have extremely high impact strength and therefore are safe and highly functional, they are used as vision corrective lenses and lenses for sunglasses and protective spectacles.
The protection of eyes from harmful ultraviolet radiation by providing ultraviolet absorptivity to spectacle lenses is strongly desired, and a coating layer having ultraviolet absorptivity is formed on the surfaces of cast lenses and glass lenses to meet this. However, the above coating method has disadvantages that these lenses become expensive and slightly yellow by themselves. An ultraviolet absorber is added before polymerization to manufacture the cast lenses. However, this method has such disadvantages as the inhibition of polymerizability and the marked yellowing of the lenses.
In contrast to this, in spectacle lenses made of polycarbonate resin, the polycarbonate resin itself has absorptivity for ultraviolet radiation on a short wavelength side and can be mixed with an ultraviolet absorber having absorptivity for ultraviolet radiation on a longer wavelength side than the ultraviolet absorption wavelength of the polycarbonate resin. However, the polycarbonate resin of the prior art can absorb ultraviolet radiation having a wavelength of up to 375 nm. To absorb ultraviolet radiation having a longer wavelength than that, a large amount of an ultraviolet absorber must be added. Since an ultraviolet absorber generally has sublimation properties, when a large amount of an ultraviolet absorber is added, it sublimes to contaminate the mirror surface of a metal mold at the time of injection molding the polycarbonate resin, thereby significantly impairing the appearance of the obtained lens.
Patent document 1 discloses a resin composition which comprises 100 parts by weight of a transparent thermoplastic resin and two different ultraviolet absorbers, one having an absorption maximum at a wavelength of 300 to 345 nm and the other having an absorption maximum at a wavelength of 346 to 400 nm. Although this resin composition was developed for spectacle lenses having excellent transparency and high ultraviolet absorptivity, as product waste is re-used in the resin composition, its color change is large when heat history such as re-extrusion is added and its resistance to molding heat is not satisfactory.
Patent document 2 discloses a resin composition which comprises polycarbonate resin, two different ultraviolet absorbers and a lactone-based heat stabilizer. However, it is said that the lactone-based heat stabilizer colors when it receives heat history, and it is reported that when it is added to polycarbonate resin, the color of the resin does not become stable.
Patent document 3 discloses a polycarbonate resin composition for rotational molding which contains a phosphorus-based stabilizer, a phenolic antioxidant and a sulfur-based antioxidant. Stated more specifically, it discloses a resin composition which comprises polycarbonate resin, a phosphorus-based heat stabilizer, a phenolic antioxidant, a sulfur-based antioxidant, a benzotriazole-based ultraviolet absorber and a release agent. However, the color and ultraviolet absorptivity of the resin composition are not satisfactory for spectacle lens application.    (Patent document 1) JP-A 09-263694    (Patent document 2) WO2005/069061    (Patent document 3) JP-A 2002-020607